I think they're for superfans, but, I have to say...many of the extra scenes were cut for time, not because they were "bad". That's my opninion at least. But, if you disliked them the first time around, doubt the extra scenes will make a difference.

The only thing about Avatar that doesn't have me completely stoked right now is Cameron's choice to use Weta studios over ILM. Now, I believe he went with them because they currently have the most advanced performance-capture studios on the planet, but outside of that, I aint a fan.